I just had my '91 300E front flex disk replaced. While I was there, the mechanic said that I should probably have a transmission fluid service/replacement as it appeared the fluid was old. Not knowing when the last time was that the transmission oil was replaced, I agreed and now regret it! When I drove it home, I noticed a small puddle of fluid underneath the car under the transmission torque converter. I asked the mechanic about it and he said that it was normal due to having to remove so many items during the whole process but that the leaks should stop after no more than a couple of days. I remembered that the day after the initial transmission service, I checked the fluid level when hot with engine running and found that it was about 1/8 inch over the top mark. About a week later, I checked the fluid again and it was in the middle mark. Ironically, the transmission now doesn't flare at all, shifts perfectly and has never been better but the leak now makes me nervous. I took it in today and the mechanic stated that it was probably that the drain plug was loose and to drive it around for a while to see if it starts leaking again. Otherwise, the O ring and seals need to be replaced. Why is it that I read here that as soon as someone takes in their car for a transmission service, a very common problem afterward is fluid begins leaking?? Is there a common mistake made during the process? My 300E is a 2.6 litre, but I had it debadged and wonder now if they accidentally used parts for a 3.0 litre instead? They said that they could also tell that my original transmission had been replaced in the last 2-3 years and that a smaller than normal transmission was used in its place.....what does that mean?? A 190 tranny perhaps??

Help!